Hydrocarbon reaction



Patented June 10, 1941 I 2,245,038 HYDROCARBON REACTION Melvin M. Holm,San Francisco, and Eugene H.

Oakley, El Cerrito, Calif., assignors to Standard Oil Company ofCalifornia, San Francisco, Calif., a corporation of Delaware ApplicationOctober 14, 1940, Serial No. 361,084

11 Claims.

This invention relates to an improved process for the alkylation ofisoparafiins with oleflns by means of a liquid acid catalyst, and moreparticularly to said process when employed for the production of liquidmotor fuels of high antiknock value. I

This application is a continuation-in-part of our copending applicationSerial No. 282,724, filed July 3, 1939.

It is known that the isoparaflinic hydrocarbons, such as isobutane andisopentane, may be caused to react with the normally gaseous olefins,such as propylene and the butenes, by means of liquid acid catalysts,such as concentrated sulfuric acid. The products of the reactioncorrespond in substantial part to the union ofone molecule ofisoparaflin with one molecule of olefin and are usually referred to asalkymers. The alkymers produced from the isoparafiins and olefinscontaining less than six carbon atoms per molecule have a high antiknockvalue and are therefore particularly desirable in the preparation ofmotor fuels.

It has been found that while the above alkylation reaction of, forinstance, isobutane by a butene is at first readily catalyzed byconcentrated sulfuric acid, the acid soon becomes inactive, apparentlydue to the accumulation of the products of side reactions, and thealkylation reaction substantially stops. Accordingly, alkylation may beefiected by charging a batch of acid to an appropriate alkylatingsystem, using it until its catalytic activity is spent and thendiscarding it. Such a batch or' intermittent method of operation is,however, not well adapted to'large scale commercial operation and theconsumption of acid by this method is so high 'as to be entirelyuneconomical in the production of alkymers for motor fuel.

It is the broad object of the present invention toprovide an entirelycontinuous process for the alkylation of isoparamns with oleflns bymeans of a liquid acid catalyst.

It is a more specific object of the present invention to provideacontinuous process for the alkylation of isoparafllns'with oieflns bymeans of a liquid acid catalyst which is economical of acid 1 and welladapted to large scale commercial operation.

It is a still more specific object of the present invention to provide acontinuous process for the manufacture of isoparaflinic motor fuels ofhigh "antiknock-value by alkylating isoparamnsof less than six carbonatoms with normally gaseous olefins by means of a liquid acid alkylationcata lyst, such as concentrated sulfuric acid.

Other and further important objects of the invention will becomeapparent from the following description and the appended claims.

While it is to be understood that we are not to be limited to any meretheoretical explanation, as mentioned above, the deterioration of anacid alkylation catalyst, such as su1furic acid, is ap; parently due tothe formation and accumulation of certain hydrocarbon compoundsresulting from reactions which accompany the main alkylation reaction.These hydrocarbon compounds apparently enter into complex combinationwith the acid molecules and thus interfere with their ability tocatalyze the alkylation reaction. We'

placed by fresh acid, this rapid-loss ofccatalytic. activity may beentirely prevented and the catalyst maintained active for promoting thealkylation reaction for very long periods of time.

It will thus be apparent that the process of our invention relates tothe alkylation of isoparaflins with clefins by contacting saidisoparaflins and olefins together or in appropriate sequence with aliquid acidalkylation catalyst which is being continually replenishedwith' fresh. acid, thus making possible an operation which is entirelycontinuous and adapted to commercial use.

In our copending application Serial No. 282,724 it was disclosed that bymaking-this rate of replenishment such that the concentration of freeacid in the catalyst is maintained constantly above a critical minimumvalue its alkylating ability may be kept in the above-mentioned constantrange and the rapid loss of efliciency may be entirely prevented, thusmaking possible a truly continuous process in which the acid consumptionis not excessive. We have now discov-- ered that when, in addition,certain ratios of acid to hydrocarbon are maintained in the severalreaction zones of the process disclosed the consumption of catalyst acidmay be still further reduced;

in our process as disclosed three distinct zones are present. In thefirst the isoparafiin, olefin and acid catalyst are intimately mixed andthoroughly contacted by violent mechanical agitation and the alkylationreaction is thereby largely completed in this zone. The second is a dualpurpose zone of residual reaction and of primary separation ofhydrocarbons from the acid catalyst while the third is a substantiallyquiescent zone of final separation.

According to one embodiment 'of the process .of the present inventionthe ratio of acid to hydrocarbon maintained under conditions of reactionin the first two zones is materially lower than in previously known'alkylation processes and hence the rate of acid deterioration and theexpenditure of acid per unit of product is substantially reduced. Thisis accomplished by maintaining a high ratio of acid catalyst tohydrocarbon reactants in the first zone of major reaction, which ispreferably of restricted volume and cross-section relative to the secondzone, and maintaining a much lower ratio in the second or residualreaction zone. The ratio of total acid to hydrocarbon in the two zonesunder reaction conditions is thus materially less than is neces- 'saryin the initial zone of primary reaction. This is in contrast to the moreusual process in which the relatively high proportion of acid requiredin the zone of initial reaction is maintained throughout the wholeregion of reaction.

The'invention will be further explained with particular reference tosulfuric acid as the liquid alkylation catalyst and the alkylation ofisobutane with butene for the production of aviation motor fuel of highantiknock value as the alkyla- ,chlorosulfomc acid, and to mixed liquidacid alkylation catalysts, such as sulfuric and phosphoric, sulfuric andchlorosulfonic acids, etc.,

and to other alkylation combinations, such as isobutane with propylene,isopentane with butene, isopentane with propylene, etc.

The point at which sulfuric acid rapidly loses its ability to catalyzethe alkylation of isoparaflins with olefins will depend somewhat onthe-temperature at which the alkylation reaction is effected, theconcentration of the original acid, the composition of the hydrocarbonfeed sub-. jected to alkylation, etc. Starting with commercial acidcontaining 96 to 98% H2804, and alkylating isobutane with butene, wehave found that the titrated acidity of the acid catalyst, substantiallyfree of butyl acid sulfate, progressively decreases .to about 86% byweight, calculated as H2804. as more fully explained hereinafter, whilethe rate of alkylation and the quality of alkymers produced remainsubstantially constant. If the reaction is then continued furtherwithout the addition of fresh acid, the gravity and theacidity of thecatalyst decrease very rapidly while both the yield. and the quality ofalkymers produced fresh acid whereby the catalyst is maintained highlyactive for meeting the alkylation of isopara'flins with olefins, theconsumption of acid is materially decreased and the quality and yield ofsmall portion of the acid.

When the concentration of the acid catalyst is so controlled it has beenfound desirable to maintain the volume ratio of acid to hydrocarbonreactants in the-initial reaction zone of restricted volume, in which amajor part of the alkylation reaction is effected under violentmechanical agitation, at about one to one or above. It has, however,been found possible toreduce this ratio in the subsequent zone ofresidual reaction and relatively larger volume to about one to five andsometimes as low as one to ten. By thus maintaining a substantiallyreduced proportion of acid catalyst in the zone of residual reaction andinitial separation and by, at the same time, keeping the zone of initialreaction and high acid content less than half of the total reactionspace, the quantity of acid catalyst that is continuously under reactionconditions is very substantially less than in previously disclosedprocesses and hence the rate of utilization of acid per unit of productis correspondingly reduced.

This invention may be better understood by reference to the accompanyingdrawing wherein one specific embodiment exemplifying the invention isshown. In this embodiment a mixture of hydrocarbons containing anisoparaflin, to be alkylated, such as isobutane, and the olefin foreffecting the alkylation, such as butene, is introduced through line Iand valve 2 to a mixing device 4 which may be in any convenient form,such as a centrifugal pump or turbo-mixer or other instrumentality foreffecting a high degree of dispersion of one immiscible liquid inanother. Acid catalyst is added through line 3 and isoparaflin recycledfrom the process, as presently to be described, through line 6 and valve26. The hydrocarbon reactants are thoroughly mixed with theacid'catalyst by the violent mechanical agitation effected in 4 and themixture is then discharged through a further contacting and cooling zoneI, provided with baflles or other elements for effecting turbulence, andis then led through line 8 to a residual zone of reaction and initialseparating chamber 9 wherein the acid catalyst tends to separate bygravity from the hydrocarbon phase. From the chamber 9 a hydrocarbonphase, which may contain some dispersed acid, is taken through a hoodeddrawofl 40 into line H) and through valve ll to a final zone ofseparation if,

the acid collectedtherein being indicated by 12a.

From'separator l2 the substantially acid-free hydrocarbon reactionmixture may then be led through line l3 and valve M to a stabilizer I5,equipped with an appropriate heating element I6 and a refluxing deviceI'I, wherein the alkymer product may be freed from C4 and lighterhydrocarbons. If the hydrocarbon raw material charged to the processcontained both normal and isobutane the overhead from stabilizer l5 maybe led through line .20 to a butane still 2|, equipped with heatingelement 22 and reflux element 23 wherein the isobutane is separated fromthe normal butane and led back to the initial alkylation zone throughline 8, condenser 4| and valve 26 for further reaction while the normalbutane is discharged from the system through valve 24 and line 25. malbutane is present the overhead from stabilizer I! may be led directlythrough valve Q! I In the event that honor-' separate by gravity fromthe reaction mixture in vention this separation is not permitted toreach the point at which a continuous acid phase is I formed, a mixtureof hydrocarbon and coarsely dispersed acid catalyst being led from thebottom of the chamber 9 through line 29, valves 30 and 3| and line 3 foradmixture with fresh reactants and return to the zone of primaryreaction in mixer 4 and contactor I. By regulating the rate of passageof the reaction mixture through the zone of residual reaction andinitial separation in chamber 9 and by adjusting the relative rates ofhydrocarbon removal through line l and hydrocarbon and acid removalthrough line 29, it is possible to keep the acid content of the streamremoved through line 10 at a low value, usually not over a few per cent,while the acid content of the mixture passing through line 29 may be of.

the order of 50 to 60%. It is thus possible to maintain any desired highratioof acid to hydrocarbon, as for instance one to one by volume orabove, in the zone of initial alkylation comprising mixer 4 andcontactor-cooler I, while maintaining a substantially lower ratio in thezone of residual reaction and primary separation in chamber 9. In orderto derive the greatest benefit from this feature of our invention it isdesirable to keep the volume of the zone of initial I alkylation assmall a fraction as possible of the total reaction space as for instanceless than 40% and preferably not more than 10% while maintaining aratioof acid to hydrocarbon in the re- 'maining 60 to 90% of thereaction mixture of not more than 1 to 2 and preferably 1 to -10 orless.The quantity of acid maintained under reaction conditions is thusmaintained low relative to the quantity of alkymers produced as comparedwith other known alkylation processes and a substantial operatingeconomy is thus efiected;

Under some conditions it may be desirable, in order to maintain thedesired acid-hydrocarbon balance throughout the system, to recycle aportion of the hydrocarbon phase, .containing some alkymer product, fromline l0 through line 42 and valve 43 or from separator l2 through line31 and valve 38 into line 5 and mixer 4.

The acid collected in separator I2 is removed through line 21 from whichit may be returned to'the reaction zone through valve 28, line 3 andvalve 3| or may be discharged from the system through valve 3-3 and line34. Fresh acid for initially charging the system and for maintaining theconcentration and the activity of the acid in the reaction zone, asdescribed above, may be added by pump 36 through valve and line 3,

or through other convenient connection to the reaction zone.

The arrangement of the hooded drawofl'. connection through which thehydrocarbon phase is drawn from vessel 9 into line I0 is a significantfeature in the smooth operation of the processas described herein. Bylocating this element at a lower level than and on the downstream sideof the point of entry ofacid-hydrocarbon mixture into the vessel 9 theacid droplets are permitted to attain a directed velocity which servesto carry them past the hydrocarbon drawoff hood and thus produce aregion of very low acid content within the hood from which a hydrocarbonliquid substantially free of acid may be drawn, thus reducing the loadon final separator l2 to a minimum and contributing to the flexibilityofoperation of the process.-

In alkylating isobutane with normal or mixed into the settling zone 9wherein the alkylation reaction is substantially completed. It may thusbe desirable to so construct the contactor I that it may also serve as acooling device. Sufiicient pressure to maintain the hydrocarbonreactants in liquid phase is usually desirable though not absolutelynecessary.

It is also found desirable tov maintain a high ratio of isoparaffin toolefin and a high concentration of isoparafiin at the point at which theolefin first contacts the acid catalyst and throughout the zone ofactive alkylation, and for this reason the hydrocarbon charged to thesystem should contain a greater molecular proportion of isoparaflin than.olefin and the, rate of recycling isoparafiin through line 6 and valve26 should be as high as convenient. Recycle of 'the isoparafl'in richreaction mixture through lines 3 and 5, as above described, is alsouseful in maintaining the desired high ratio of isoparafiin to olefin inthe zone wherein the major portionof the alkylation reaction iseffected. It is preferred that the molecular ratio of isoparafiln toolefin at the point of mixing with the acid catalyst and in the primaryreaction zone '4 be at least about fifty to one and for the best resultsto which isobutane is added to give an appropriate ratio of isoparaflinto olefin, as described above, is alkylated according to the methoddescribed, the sulfuric acid catalyst may be maintained at maximum andsubstantially constant activity by keeping its titrated acidity aboveabout 94-95% by weight, when expressed as K280i, and its gravity aboveabout 64 B., as

more fully explained below, and that this may be accomplished by addingfresh 95 to 98%. acid at the rate of usually not more than about 1.5

pounds per'gallon of alkymer produced 'while a corresponding amount ofused acid is withdrawn."

The material which is accumulated by the acid during the course of thealkylation reaction and which is responsible for its decrease in gravityand concentration and its-ultimate loss of alkylating activity is rathercomplex in character and variable in amount, dependent upon the originalconcentration of the acid, the composition and purity of the rawmaterial and particularly the temperature of alkylation, so that it isimpossible to give an exact value of either acid concentration orgravity that must, under all conditions, be maintained in ordertomaintain a satisfactory catalytic activity. The used sulfuric acidcatalysts have been found to contain a highly unsaturatedterpene-like-hydrocarbon material and alkyl sulfonic acids, both ofwhich apparently play a part in the inactivation of the acid. Bothwould, of course, lower its gravity in proportion to the respective[quantities present while obviously only the former butenes andconcentrated sulfuric acid as the,

would lower its titrated acidity in direct proportion to the amountpresent. A used acid catalyst will aBo contain alkyl acid sulfatevarying in amount with the point the system at which it is withdrawn andalso with the specific combination of conditions being employed ineffecting the alkylation reaction. The presence of the alkyl acidsulfate; however, while it lowers the measured acidity and the gravityof the catalyst, apparently is not significant in a determination of theimmediate activity of he catalyst.

While the ultimate test of the alkylating activity of a used acidcatalyst would, of course, be to use it in a standard control alkylationreaction, we have found that a fairly reliable indication of thecondition of used sulfuric acid may be obtained from its titratedacidity or its gravity when determined in view of the foregoingcomplications. The acid withdrawn at a point in the system at which thealkylation reaction is substantially complete would contain, I

at most, only a few tenths of a per cent by weight of alkyl acidsulfate,which can be disregarded. However, in the event that acid containingmore than, for instance, 3.2 to 0.3% of alkyl acid sulfate is to beevaluated, the ester should be either removed in known manner orappropriate correctlon made for it in the gravity or acid concentrationvalues used in such evaluation.

When observing the foregoing conventions, we have -found that a Baumgravity of about 60:t2 represents the gravity above which the sulfuricacid, substantially free of alkyl acid ester, must be held, under allcombinations of conditions so far tested, in order that its activity maybe maintained for efiecting the alkylation reaction to produce a productof the highest quality. The titrated acidity of the catalyst,substantiallyalkyl acid sulfate free, while not so quick and easy a testto apply, is a somewhat more reliable indicator of the catalystactivity. In order that its highest alkylating activity may bepreserved, we have found that the titrated acidity, expressed as IIZSO,should be kept above about 86% by weight and that the range within whichthe minimum satisfactory concentration may vary with varying conditionsof operation is between about 82% and 90%.

The rate at which used acid must be withdrawn and fresh acid added inthe practice of Pounds of 96-98% Temperature, F. acid per gallon ofalkyulers 0. 2 to 0. 5 l). 3 to l. 0. 5 to 2.0 1.0 to 4. 0 Abme 3.0

While the foregoing figures are believed to cover the range of practicaloperating conditions of the various specific'rnethods of operation nowknown, it will, of course, be realized that the exact value for anyparticular method, feed composition and set of operating conditionscould only be determined by actual experiment.

Operation of the process of our invention and the advantages to bederived therefrom may be better appreciated from the following example:ExampZe.A normal C-i cut from the liquid phase cracking oi a heavypetroleum oil was passed through a polymerization plant wherein 76.5 v;or" the olefins were removed. The residual gas was enriched withisobutane until the ratio of isobutane to olefin was 3.3.? to i. Themixture was then charged to a continuous alkylation plant of the threezone type described here inabove. The fresh acid catalyst charged was98% sulfuric acid and the catalyst was maintained at about Be. (about95.5% H2804 throughout the system by continuously. replacing a smallportion of the used catalyst with fresh acid. Operation andrecirculation rates were maintained, as described, so that the isobutaneto butene ratio at the point of mixing with the acid was 515 to i, theconcentration oi isooutane in the hydrocarbon phase was 63.2% and theconcentration of acid in the primary reaction zone of high dispersionwas between so and 55% while the concentration of acid in the largevolume zone of residual reaction and initial separation was about 15% byvolume. The capacity of the primary reaction zone containing the highproportion of acid was only 15.5% of the total capacity of the two zonesof reaction so that the quantity of acid continuously under reactionconditions was only 40% of what it would have been in a conventionalsystennof the same capacity, having a constant ratio of acid to hydrocarbon throughout. Under these conditions the alkylation productamounted to by weight or the olenns charged, had a gravity of 68.0 A. P.I. and contained 99.5% of aviation gasoline having a bromine number of0.1 and an octane.

number of 96.5.

While the present invention has been explained with respect to onespecific embodiment, as set out in the drawing and described in detailabove,

' it will be appreciated that the principles of maintaining the acidcatalyst above a critical minimum strength by continuous acidreplacement and of maintaining a higher ratio of acid catalyst tohydrocarbon reactants in the zone of initial high reaction than in asubsequent zone of residual reaction-which constitute essential featuresof alkymer product, as experienced informer batch methods of operation,to an entirely practical amount between about 0.5 and 1.5 pounds pergallon of alkymers.

Having thus disclosed and exemplified our invention of an improvedprocess for continuously and economically alkylating isoparafins witholefins by means of a liquid acid catalyst, we

claim:

1. Process for the alkylation of hydrocarbons which comprisesmaintaining two zones of reaction in series, the first of which is ofsmaller capacity than the second and contains a means of mechanicalagitation for intimately contacting two immiscible liquids, continuouslycharging olefins, a molecular excess of low boiling isoparafiins andstrong sulfuric acid into the mixing device of the first reaction zonewherein the hydrocarbon and acid phases are thoroughly mixed underalkylating conditions, introducing the resulting mixture into the upperportion of an enlarged vessel constituting the second zone of reactionin which at least a partial separation of acid and hydrocarbon phases iseffected so that the acidto-hydrocarbon ratio leaving the bottom of saidenlarged vessel is higher than the average ratio existing in the vessel,maintaining a higher volume ratio of acid to hydrocarbon in the firstbutane and butene in molecular ratio above about 100 to 1 to said firstreaction zone and intimately contacting said hydrocarbon mixture withstrong sulfuricacid in the mixing device of said first reaction zonewherein the hydrocarbon and acid phases are thoroughly mixed underalkylating conditions, maintaining the proportion of acid in zone thanin the second, maintaining the acid gravity in both zones of reactionabove at least 60 B. by continuously replacing a portion of the usedacid catalyst with fresh acid, recycling a portion of the acid andhydrocarbon reaction mixture from said second zone to said first zone,withdrawing another portion of the reaction mixture from the upperportion of said second zone through a hooded connection whereby theratio of acid to hydrocarbon withdrawn may be regulated and passing saidwithdrawn mixture to a separating zone wherein acid is separated fromhydrocarbons.

. 2. Process for the alkylation of isoparafiinic hydrocarbons whichcomprises maintaining two zones of reaction in series, the first ofwhich is of smaller capacity than the second and contains a means ofviolent mechanical agitation for intimately contacting two immiscibleliquids and the second of which consists of a vessel of relatively largecross-section free from any mechanical obstruction that would materiallyinterfere with the quiet fiow of liquids therethrou'gh, continuouslycharging a normally gaseous olefin, a molecular excess of a low boilingisoparaffin and strong sulfuric acid into the mixing device of the firstreaction zone wherein 'the hydrocarbon and acid phases are thoroughlymixed under alkylating conditions, maintaining at least 50% by -volumeof acid catalyst in said first reaction zone, introducing the resultingmixtufe into the upper portion of a vessel of enlargedcross-sectionwhich constitutes the second zone of reaction, in which atleast a partial separation. of acid and hydrocarbon phases is effected,maintaining the proportion of acid to hydrocarbon in said second zone ofreaction below about 20% by volume, maintaining the acid gravity in bothzones of reaction above at least 60 B. by continuously replacing aportion of the used catalyst with fresh acid, maintaining the proportionofisoparamn in the hydrocarbon phase in both zones of reaction above 50%by volume, recycling a portion of the acid and hydrocarbon reactionmixture from said second reaction zone to said first rethe reactionmixture'in said first reaction zone at least above by volume,introducing the resulting mixture into the upper portion of the vesselof enlarged cross-section which constitutes the second zone of reaction,maintainingthe proportion of said acid to hydrocarbon in said secondzone of reaction below about 20% by volume, maintaining the acid gravityin both zones of reaction above at least B. by continuously replacing aportion of the used acid with fresh acid, maintaining the proportion ofisobutane in the hydrocarbon phase in both zones of reaction above 50%by volume, recycling a portion of the acid and hydrocarbon reactionmixture from the bottom of said'second reaction zone to said firstreaction zone and passing a second portion of the reaction mixturecontaining a lower ratio of acid to hydrocarbon from said secondreaction zone to a separating zone wherein acid separates fromhydrocarbons by gravity. 4. Process for the alkylation of isobutanewhich comprises maintaining two zones of reaction in series, the firstof which is of less than about one-fourth the capacity of the second andcontains a means of violent agitation for intimately contacting twoimmiscible liquids and the second of which consists of a vessel ofrelatively large cross-section free from any mechanical obstructionthatwould materially interfere with the quiet fiowof liquidstherethrough, continuously charging isobutane and butene in molecularratio above about to 1 to said first reaction zone and intimatelycontacting said hydrocarbon mixture with strong sulfuric acid in themixing device of said first reaction zone wherein the hydrocarbon andacid phases are thoroughly mixed under alkylating conditions,maintaining the which constitutes the second zone of reaction,

action zone and passing another portion of the reaction'mixture fromsaid second reaction zone to a separating zone wherein acid separatesfrom hy'drocarbons by gravity.

3. Process for the alkylation of isobutane which comprises maintainingtwo zones ofrreaction in series, the first of which is of smaller volumethan the second and contains a means of violent mechanical agitation forintimately contacting two immiscible liquids and the second of whichconsists of a vessel of relatively large crosssection free from anymechanical obstruction that would materially interfere with the quietfiow of liquids therethrough, continuously charging isoreaction mixturemaintaining the proportion of said acid to hydrocarbon in said'secondzone of reaction below about 20% by volume, maintaining the acid gravityin both zones'of reaction above at least 60 Be. by continuouslyreplacing a portion of the used acid with fresh acid, maintaining thepro portion of isobutane in the hydrocarbon phase in both zones ofreaction above 50% by volume, recycling a portion of the acid andhydrocarbon from the bottom of said second reaction zone to said firstreaction zone and passing a second portion of the reaction mixturecontaining a lower ratio of acid to hydrocarbon from the upper portionof said second reaction zone to a separating zone wherein acid separatesfrom hydrocarbons by gravity.

5. Process for the alkylation of, hydrocarbons which comprisesmaintaining two zones of reaca ratio of about one volume of acid pervolumeof hydrocarbon in said first zone, violently agitating the acidand hydrocarbon phases in said 1 a second zon'e which is clear ofbattles and similar obstructions free fiow whereby a partial separationof the and hydrocarbon phases is promoted, maintaining a ratio of acidto bydrocarbon in said second zone which is substantially less than inthe aforesaid first zone, recycling acid and h drocarbon from saidsecond zone to said first zone and withdrawing hydrocarbon containingalhymer roduct from said second zone to a substantially quiescent zoneof separation. r

6. Process for the alkylation of isoparaffins which comprisesmaintaining in series a first zone of primary reaction wherein reactantsare subjected to violent mechanical agitation and a second zone ofresidual reaction and primary separation under substantially lessagitation, said first zone being of smaller volume and smallercross-section than said second zone, the rate of passage of fluidreactants through said first zonethus being greater than through saidsecond zone, continuously charging isoparafiin and concentrated sulfuricacid containing alkyl acid sulfate to said first zone inquantities suchthat the molecular ratio of isoparafiin to alkyl acid sulfate is alwaysgreater than 100 to 1, passing reaction mixture from said first zone tothe upper part of said second zone, returning acid and hydrocarbon fromthe bottom of said second zone to said first zone, withdrawinghydrocarbons including alkymer product from the upper portion of saidsecond zone and maintaining the concentration of sulfuric acid in theacid phase in both zones above 94% by weight HzSO z by continuouslyreplacing a small portion of it with fresh strong acid.

.7. In a process for the alkylation of isoparaffins with olefins bymeans of an acid alkylation catalyst, the improvement which comprisesmaintaining two zones of reaction in series, maintaining theconcentration of isopa'rafiin to be alkylated at least about 50% byliquid volume of the hydrocarbon phase in said first zone and effectingtherein a high degree of dispersion between relatively immiscible acidalkylation catalyst and hydrocarbon phases to produce a large surface ofcontact therebetween in order to expedite the alkylation ofisopara-ifins in the hydrocarbon phase with components in the acidcatalyst phase, introducing the resulting mixture into said second zonein which said dispersed acid catalyst the hydrocarbon phases aresubjected to a force tending to efiect a separation therebetween due tothe relative difierence in densities between said two phases resultingin an increase of the volume ratio of acid catalyst to hydrocarbon inthe mixture in said second zone in the direction of said force,maintaining a higher vol- Lune ratio of acid catalyst to hydrocarbon insaid zone than the average volume ratio of acid catalyst to hydrocarbonin said second zone, recycling a portion of the acid catalystandhydrocarbon migture from a location in said second zone wheretheratio of acid catalyst to hydrocarbon is hi her than the average insaid second zone, withdrawing another portion of the reaction mixturefrom'a location in said second zone where the acid catalyst tohydrocarbon ratio is lower than at said first-mentioned location, andpassing said portion so withdrawn to a separating zone where acidcatalyst is separated from hydrocarbons.

8. Process as defined in claim 7 in which the volume ratio of acidcatalyst to hydrocarbon maintained less than about 1 to 5 in said secondzone.

9. Process as defined in claim '7 in which saidother portion of thereaction mixture is withdrawn from where in said second zone the acidcatalyst to hydrocarbon ratio is lower than the average in said secondzone.

10. In a process for the alkylation of isoparships with olefins by meansof an acid alkylation catalyst the improvement which comprises-maintaining two zones of reaction in series,

maintaining the concentration of isoparaifin to be alkylated at leastabout 50% by liquid volume of the hydrocarbon phase in said first zoneand said dispersed acid catalyst and hydrocarbon phases tend to separateby gravity resulting in a gradual increase of the volume ratio of acidcatalyst to hydrocarbon downwardly in the mixture in said second zone,maintaining a higher volume ratio of acid catalyst to hydrocarbon insaid first zone than the average volume ratio of catalyst to hydrocarbonin said second zone, recycling a portion of the acid catalyst andhydrocarbon mixture from where in said second zone the ratio of acidcatalyst to hydrocarbon is higher than the average in said second zone,withdrawing another portion of the reaction mixture from where in saidsecond zone the acid catalyst to hydrocarbon ratio is lower than theaverage in said second zone, and passing said portion so withdrawn to aseparating zone where acid catalyst is separated from hydrocarbons.

11. Process as defined in claim 10 in which the volume ratio of acidcatalyst to hydrocarbon is maintained less than about 1 to 5 in saidsecond zone.

MELVIN M. HOLM. EUGENE H. OAKLEY.

